Following the questionable 1804 Treaty, the fallout from the 1814 Battle of the Rock Island Rapids, and subsequent establishment of Fort Armstrong in 1816, tensions with local native populations were at a peak. Continued spats of engagements between settlers, Rangers, and Soldiers continued with isolated killings up thru 1832. Fort Armstrong had been established to reduce the amount of these interactions, monitor Sauk and Fox activities west of the Mississippi River and enforce the 1804 treaty. Just downriver from the fort sat the Sauk capital village of Saukenuk at the confluence of the Rock and Mississippi Rivers.

The preceding years of 1829 thru 1831 were difficult for the Sauk and Fox. Poor growing and hunting seasons, coupled with various demands and perceptions of favoritism for other tribes by the Americans, colored Black Hawk’s vision. By 1832, he was explicitly being told to not cross back east of the Mississippi River, contradicting the 1804 treaty which had allowed the tribes to occupy limited protected sites, such as Saukenuk. But Black Hawk believed that he still was legally allowed to cross back to Saukenuk, and this, together with encouragement from the Winnebago leader Prophet, led to his fateful decision to cross the river.

On 5 April 1832, Black Hawk, accompanied by 1,500 other Sauk and Fox, crossed the Mississippi River near Saukenuk. Of the 1,500, approximately 500 were warriors, with the remaining being women, children, and the elderly. After crossing, they proceeded up the eastern bank of the river, having found Saukenuk largely occupied by American squatters. The majority of his group moved by canoe, while the warrior group moved over land. They had decided to make for the Winnebago village to the northeast and meet with the Prophet, who had supposedly sought an alliance against the Americans.

Upon meeting with the Prophet, Black Hawk discovered that he had no such interest, nor was he able to provide any assistance to Black Hawk in evading his pursuers. Black Hawk eventually tried to escape with his band back across the Mississippi but could not do so by way of the Rock River. Though the Americans were disorganized, they were able to follow Black Hawk up he river and cut off his routes south and west. This forced him to attempt to escape to the north. General Henry Atkinson, commander of the forces at Fort Armstrong, was tasked by Illinois Governor John Reynolds with capturing Black Hawk. However, Atkinson was reluctant to do so since he believed that Black Hawk had not broken any laws.

By the end of April, Black Hawk’s resources had dwindled, and Atkinson was aware of this due to open communication between himself and Black Hawk. Atkinson had attempted to delay the deployment of forces, but eventually elements of the organized militia were successful in their pursuit of Black Hawk’s men. On 14 May, Major Isaiah Stillman and his men made hostile contact with Black Hawk’s band, which ended any chance of a peaceful resolution.

On 2 August, Atkinson’s main force had caught up to Black Hawk and his men north of Prairie du Chien, Wisconsin. In the ensuing battle, Black Hawk was captured and many of his followers were killed. Of the original band of 1,500, approximately 160 survived and escaped across the Mississippi. Black Hawk was subsequently sent to Washington and forced to live out his days largely disconnected from the reservation lands. He died in 1838 shortly after composing his memoirs. With the Sauk and Fox relocated well on the western side of the Mississippi, Fort Armstrong’s mission was accomplished, and it was subsequently abandoned. The frontier of the United States now was pushed out beyond the divide of the mighty river that bisected the country, and settlers had become more numerous and able to defend themselves in the region.